The invention relates generally to printing and, more particularly, to the formation of an image on a copy sheet with a printing master.
Methods for making copies from printing masters are known wherein the printing master is provided with characters to be transferred or copied. The characters are mirror-reversed from the images formed thereby on the copy sheet or duplicating sheet and are made of a material which includes leucauramine. Here, a copy sheet is used which is provided on both sides thereof, that is, on the side to be printed and on the side opposite the latter, with a layer of attapulgite, the copy sheet being moistened prior to the printing operation. The images formed on the copy sheet are a result of a reaction which occurs due to the presence of three components, namely, the leucauramine, the attapulgite and the liquid used for moistening the copy sheet. To print a copy sheet, the printing master is set into rotation and a counter-pressure roller is used to urge the moistened copy sheet into contact therewith.
It has, however, been found that the use of a copy sheet provided with a layer of attapulgite on opposite sides thereof possesses a serious disadvantage when a machine having an automatic feeder for feeding the copy sheets to the printing master is utilized. Thus, if a misalignment of one copy sheet occurs so that this is not conveyed to the printing location or, at least, is not conveyed to the printing location at the requisite time, the still-rotating printing master will contact the counter-pressure roller. As a result, some of the material which constitutes the mirror-reversed characters on the printing master will be transferred to the counter-pressure roller. Consequently, the next copy sheet to be conveyed to the printing location will be printed on its back side, that is, the side opposite to that which it is desired to print with the printing master, by the counter-pressure roller. This is a result of the moistening or soaking of the copy sheet which is performed prior to the printing operation and which now assures that the three components necessary for the printing reaction are present at the back side of the copy sheet. Thus, a reaction occurs between the attapulgite-containing back side of the copy sheet and the leucauramine images transferred to the counter-pressure roller.
An attempt has been made to overcome the above problem by using paper carrier sheets provided with an attapulgite layer on one side only. However, this has not provided a satisfactory solution to the problem. First of all, the carrier sheet itself contains substances which are capable of reacting with the leucauramine of the printing master. Although such substances are present in the carrier sheet in much smaller amounts than in the layer provided on the carrier sheet, it is nevertheless true that faint images may be formed on the carrier sheet. Furthermore, carrier sheets having an attapulgite layer on one side only possess the tendency to curl up in one direction when the carrier sheets are provided with a layer in amounts which correspond to between 8 and 12 grams per square meter of surface area. This is particularly true when the humidity of the air changes. Consequently, it became impossible to satisfactorily convey the copy sheets by means of the automatic feeders in printing machines. In addition to the above, there arose the problem that the layman operating the machine could not tell the layered and unlayered sides of the copy sheets apart so that the copy sheets were often inserted in the printing machine in the wrong orientation.